1. Field of the Invention
The present invention relates to a fuel cell humidification system and particularly relates to a fuel cell humidification system which allows safe operation of the fuel cell under optimum conditions at the time of re-starting the fuel cell.
2. Background Art
Conventionally, a fuel cell provided with a solid polymer membrane is known. In such a type of fuel cell, power is conducted by electrons generated by a chemical reaction between externally supplied oxygen and hydrogen, flowing in the solid polymer membrane. In order to conduct efficient power generation, the solid polymer membrane should be highly conductive so that resistance to the movement of electrons generated by the reaction should be sufficiently low.
The reaction in the fuel cell generates water, and gas discharged from the fuel cell after the reaction contains a considerable amount of moisture. Accordingly, as disclosed in Japanese Patent Application. First Publication No. Hei 6-132038, a humidification apparatus for humidifying a reaction gas used for the reaction in the fuel cell is proposed by applying the gas discharged after the reaction as a humidification gas.
However, although the above-described conventional humidification system is advantageous in utilizing the discharged gas effectively, the problem arises in this humidification system that, when the atmospheric temperature in that humidification system falls due to stopping of the fuel cell, the moisture held in the lines of the fuel cell and the humidification system condenses. Accordingly, since the humidity in the fuel cell is decreased, the problem arises that the dew-point in the fuel cell becomes lower than that required for the normal operation and the insufficient humidity leads to the low efficiency of the fuel cell.
Therefore, the object of the present invention is to provide a fuel cell humidification apparatus, capable of providing the optimum operation of the fuel cell when the fuel cell is restarted.
According the first aspect, a fuel cell humidification system comprising, a fuel cell (for example, the fuel cell 1 in the embodiment) provided with an air supply line (for example, the air supply line 3 in the embodiment) for supplying air to said fuel cell and a gas discharge line (for example, the gas discharge line 5 in the embodiment) for discharging gas discharged from the fuel cell, a humidification apparatus (for example, the humidification apparatus 6 in the embodiment) including a heater (for example, the heater 21 in the embodiment) disposed across both of said air supply line and said gas discharge line connected to the fuel cell for humidifying air to be supplied to said fuel cell by water content in said gas discharged from said fuel cell, a control device (for example, the control device 27 in the embodiment) for overall control of the fuel cell humidification system, an air pressure device (for example, the supercharger 16 and the motor 16 in the embodiment) disposed in said air supply line upstream of the humidification apparatus for supplying air, a switching device (for example, the three way valve 25a in the embodiment) disposed in said air supply line upstream of said humidification apparatus and a switching apparatus (for example, the three way valve 25b in the embodiment) disposed in said gas discharge line downstream of said humidification apparatus, and a communication line (for example, the communication line 26 in the embodiment) for communicating said air supply line and said gas discharge line by connecting through said switching device of said air supply line and said switching device of said gas discharge line.
In the above fuel cell humidification system, said fuel cell comprises a solid polymer membrane functioning as a solid electrolyte and a conductivity meter attached to said solid polymer membrane for measuring humidity of said solid polymer membrane.
In the above fuel cell humidification system, the fuel cell humidification system further comprises a thermometer disposed close to said fuel cell in said air supply line.
In the above fuel cell humidification system, the pressure device comprises a supercharger and a motor for driving said supercharger.
In the fuel cell humidification system, the switching device in the air supply line comprises a three way valve with a valve control switch for opening or closing the air supply line or communicating the air supply line with the communication line, and the switching device in the gas discharge line comprises a three way valve with a valve control switch for opening or closing said gas discharge line or communicating said gas discharge line with said communication line.
According to another aspect, the fuel cell humidification system provided with the humidification apparatus for humidifying dry air used for a reaction in a fuel cell by water content of a gas discharged from said fuel cell after the reaction, comprises, an air supply line for supplying air to the fuel cell through a air pressure device; a discharge line for discharging said gas discharged from the fuel cell; a control device for overall control of the fuel cell humidification system; a humidification apparatus having a heater provided across both of said supply line and said discharge line; an air pressure device disposed in said air supply line for supplying air to the fuel cell through said humidification device; switching devices provided in said air supply line and in said gas discharge line for switching opening, closing said lines or communicating both lines, wherein, said control device controls switching devices in said air supply line and in said gas discharge line so as to communicate said supply line and said gas discharge line by forming a closed loop and the closed loop is maintained in the closed state when the fuel cell is stopped; and wherein, when said fuel cell is restarted, said control device actuates said air pressure device and said heater for adjusting the dew point of the supply air by circulating air retained in the closed loop and subsequently opens the closed loop and drives the fuel cell in the normal operation.
With the above arrangement, when the fuel cell is stopped, the closed loop is formed by communicating the air supply line and the gas discharge line so as to retain the water content in the system, so that the water content can be contained in the system even when the water content is decreased by condensation of water due to decreasing temperature. When the fuel cell is restarted, the supercharger and a heater are actuated while the closed loop is maintained in the closed state for mixing and heating the air in the closed loop such that the dew point of the air in the system can be recovered, allowing the normal operation of the fuel cell when the closed loop is released.
In the fuel cell humidification system, when the fuel cell is restarted, said control device outputs a restarting signal for actuating the air pressure device and turning on the heater while the closed loop is maintained in the closed state so that the gas temperature in the closed loop is raised and the dew-point of air to be supplied to the fuel cell is raised so as to control the humidity of the solid polymer membrane in a predetermined range while monitoring the humidity by the conductivity meter.
According to the other aspect, a fuel cell humidification method according to claim 6 comprising the steps of: communicating the air supply line and the gas discharge line with the communication line by switching devices so as to form a closed loop including the fuel cell and the humidification apparatus when the fuel cell is stopped, and when the fuel cell is restarted, actuating the pressure device by the motor while the closed loop is maintained in the closed state and turning the heater on by the heater switch for raising the dew-point of the air supplied to the fuel cell while detecting the gas temperature by the thermometer, detecting humidity of said solid polymer membrane by use of the conductivity meter, when the solid polymer membrane attains a predetermined humidity, starting the fuel cell by no-load operation after opening the three way valves for opening the closed loop, and switching the fuel cell from no-load operation to the normal load operation under load.
According to still other aspect, a computer readable recording medium including a program for executing a fuel cell humidification method comprising the steps of: communicating said air supply line and said gas discharge line with the communication line by switching said switching devices so as to form a closed loop including the fuel cell and the humidification apparatus when the fuel cell is stopped; and when said fuel cell is restarted, actuating the air pressure device while the closed loop is maintained in the closed state and turning said heater on by a heater switch for raising the gas temperature while detecting the gas temperature by the thermometer; detecting the humidity of the solid polymer by use of the conductivity meter; predetermined humidity of said solid polymer membrane is attained, starting said fuel cell by no-load operation after switching the three way valves for opening the closed loop; and switching said fuel cell from no-load operation to the normal load operation under load.